[llvm] r203489 - MemCpyOpt: When merging memsets also merge the trivial case of two memsets with the same destination.

[Benjamin Kramer]

Author: d0k
Date: Mon Mar 10 16:05:13 2014
New Revision: 203489

URL: http://llvm.org/viewvc/llvm-project?rev=203489&view=rev
Log:
MemCpyOpt: When merging memsets also merge the trivial case of two memsets with the same destination.

The testcase is from PR19092, but I think the bug described there is actually a clang issue.

Modified:
    llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
    llvm/trunk/test/Transforms/MemCpyOpt/form-memset.ll

Modified: llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp?rev=203489&r1=203488&r2=203489&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp Mon Mar 10 16:05:13 2014
@@ -75,6 +75,13 @@ static bool IsPointerOffset(Value *Ptr1,
                             const DataLayout &TD) {
   Ptr1 = Ptr1->stripPointerCasts();
   Ptr2 = Ptr2->stripPointerCasts();
+
+  // Handle the trivial case first.
+  if (Ptr1 == Ptr2) {
+    Offset = 0;
+    return true;
+  }
+
   GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
   GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
 

Modified: llvm/trunk/test/Transforms/MemCpyOpt/form-memset.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MemCpyOpt/form-memset.ll?rev=203489&r1=203488&r2=203489&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/MemCpyOpt/form-memset.ll (original)
+++ llvm/trunk/test/Transforms/MemCpyOpt/form-memset.ll Mon Mar 10 16:05:13 2014
@@ -272,3 +272,15 @@ define void @test9() nounwind {
 ; CHECK-LABEL: @test9(
 ; CHECK: call void @llvm.memset.p0i8.i64(i8* bitcast ([16 x i64]* @test9buf to i8*), i8 -1, i64 16, i32 16, i1 false)
 }
+
+; PR19092
+define void @test10(i8* nocapture %P) nounwind {
+  tail call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 42, i32 1, i1 false)
+  tail call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 23, i32 1, i1 false)
+  ret void
+; CHECK-LABEL: @test10(
+; CHECK-NOT: memset
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 42, i32 1, i1 false)
+; CHECK-NOT: memset
+; CHECK: ret void
+}